690 research outputs found
Perturbation Analysis of the Kuramoto Phase Diffusion Equation Subject to Quenched Frequency Disorder
The Kuramoto phase diffusion equation is a nonlinear partial differential
equation which describes the spatio-temporal evolution of a phase variable in
an oscillatory reaction diffusion system. Synchronization manifests itself in a
stationary phase gradient where all phases throughout a system evolve with the
same velocity, the synchronization frequency. The formation of concentric waves
can be explained by local impurities of higher frequency which can entrain
their surroundings. Concentric waves in synchronization also occur in
heterogeneous systems, where the local frequencies are distributed randomly. We
present a perturbation analysis of the synchronization frequency where the
perturbation is given by the heterogeneity of natural frequencies in the
system. The nonlinearity in form of dispersion, leads to an overall
acceleration of the oscillation for which the expected value can be calculated
from the second order perturbation terms. We apply the theory to simple
topologies, like a line or the sphere, and deduce the dependence of the
synchronization frequency on the size and the dimension of the oscillatory
medium. We show that our theory can be extended to include rotating waves in a
medium with periodic boundary conditions. By changing a system parameter the
synchronized state may become quasi degenerate. We demonstrate how perturbation
theory fails at such a critical point.Comment: 22 pages, 5 figure
Quasi regular concentric waves in heterogeneous lattices of coupled oscillators
We study the pattern formation in a lattice of coupled phase oscillators with
quenched disorder. In the synchronized regime concentric waves can arise, which
are induced and increase in regularity by the disorder of the system. Maximal
regularity is found at the edge of the synchronization regime. The emergence of
the concentric waves is related to the symmetry breaking of the interaction
function. An explanation of the numerically observed phenomena is given in a
one-dimensional chain of coupled phase oscillators. Scaling properties,
describing the target patterns are obtained.Comment: 4 pages, 3 figures, submitted to PR
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Altered chemomechanical coupling causes impaired motility of the kinesin-4 motors KIF27 and KIF7.
Kinesin-4 motors play important roles in cell division, microtubule organization, and signaling. Understanding how motors perform their functions requires an understanding of their mechanochemical and motility properties. We demonstrate that KIF27 can influence microtubule dynamics, suggesting a conserved function in microtubule organization across the kinesin-4 family. However, kinesin-4 motors display dramatically different motility characteristics: KIF4 and KIF21 motors are fast and processive, KIF7 and its Drosophila melanogaster homologue Costal2 (Cos2) are immotile, and KIF27 is slow and processive. Neither KIF7 nor KIF27 can cooperate for fast processive transport when working in teams. The mechanistic basis of immotile KIF7 behavior arises from an inability to release adenosine diphosphate in response to microtubule binding, whereas slow processive KIF27 behavior arises from a slow adenosine triphosphatase rate and a high affinity for both adenosine triphosphate and microtubules. We suggest that evolutionarily selected sequence differences enable immotile KIF7 and Cos2 motors to function not as transporters but as microtubule-based tethers of signaling complexes
ESTABLISHING PEER-COUNSELING THROUGH PEER INTERPERSONAL COMMUNICATION IN THE SCHOOL ENVIRONMENT
Student problems at school are often being a hot topic that never ends in the school environment. 70% of the average student in school ever had problems, including, family problems, social conflict, behavioral deviations, economic problems, difficulties in understanding lessons, health problems, pressure from others and problems of self-competence and self-confidence. The results of interviews with school counselors, showed a significant decrease in academic achievement with an increase in cases that occurred or experienced by students at school. Teachers, school principals and school counselors are always required to immediately resolve problems that occur to students as soon as possible without having risks that an impact on the negative image of the institution / school and damage the performance imagery that has been obtained by the institution with great struggle and hard work. To maintain the achievement, the school will impose sanctions on students who violate school rules or commit uncommon breaking norm in school or outside school with various punishments to them. On the other hand, providing rewards / prizes for those who have great achievement in academics and non-academics to make the institution / name of the school became famous and outstanding. The results of the study the influence of peer interpersonal communication on increasing student academic success is quite high in some high schools in the Pontianak city by 77% of the total 264 respondents. Various efforts to prevent and resolve student problems are carried out by school counselors in handling various cases that occur in the school environment through observation, dialogue and long discussions with counselors in the school. Researchers traced cases that occurred at schools in Pontianak and studied counseling guidance programs implemented at schools in helping educational institutions / schools guide, direct and assist students in overcoming various problems that they faced. Through peer counseling activities and optimizing peer interpersonal communication in the student environment at school. The researcher conducted a survey of several schools in Pontianak, including High School, Vocational High School and Madrasah Aliyah (Islamic high school), by conducting observations and interviews with students and school counselors on the formation of peer-counseling in the school environment through interpersonal peer communication that exists in teaching and learning process activities and non-academic activities in schools. Article visualizations
The complex network of global cargo ship movements
Transportation networks play a crucial role in human mobility, the exchange
of goods, and the spread of invasive species. With 90% of world trade carried
by sea, the global network of merchant ships provides one of the most important
modes of transportation. Here we use information about the itineraries of
16,363 cargo ships during the year 2007 to construct a network of links between
ports. We show that the network has several features which set it apart from
other transportation networks. In particular, most ships can be classified in
three categories: bulk dry carriers, container ships and oil tankers. These
three categories do not only differ in the ships' physical characteristics, but
also in their mobility patterns and networks. Container ships follow regularly
repeating paths whereas bulk dry carriers and oil tankers move less predictably
between ports. The network of all ship movements possesses a heavy-tailed
distribution for the connectivity of ports and for the loads transported on the
links with systematic differences between ship types. The data analyzed in this
paper improve current assumptions based on gravity models of ship movements, an
important step towards understanding patterns of global trade and bioinvasion.Comment: 7 figures Accepted for publication by Journal of the Royal Society
Interface (2010) For supplementary information, see
http://www.icbm.de/~blasius/publications.htm
Momentum and Heat Transfer in a Laminar Boundary Layer with Slip Flow
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77059/1/AIAA-22968-756.pd
Structural Kinetic Modeling of Metabolic Networks
To develop and investigate detailed mathematical models of cellular metabolic
processes is one of the primary challenges in systems biology. However, despite
considerable advance in the topological analysis of metabolic networks,
explicit kinetic modeling based on differential equations is still often
severely hampered by inadequate knowledge of the enzyme-kinetic rate laws and
their associated parameter values. Here we propose a method that aims to give a
detailed and quantitative account of the dynamical capabilities of metabolic
systems, without requiring any explicit information about the particular
functional form of the rate equations. Our approach is based on constructing a
local linear model at each point in parameter space, such that each element of
the model is either directly experimentally accessible, or amenable to a
straightforward biochemical interpretation. This ensemble of local linear
models, encompassing all possible explicit kinetic models, then allows for a
systematic statistical exploration of the comprehensive parameter space. The
method is applied to two paradigmatic examples: The glycolytic pathway of yeast
and a realistic-scale representation of the photosynthetic Calvin cycle.Comment: 14 pages, 8 figures (color
Two binding partners cooperate to activate the molecular motor Kinesin-1
The regulation of molecular motors is an important cellular problem, as motility in the absence of cargo results in futile adenosine triphosphate hydrolysis. When not transporting cargo, the microtubule (MT)-based motor Kinesin-1 is kept inactive as a result of a folded conformation that allows autoinhibition of the N-terminal motor by the C-terminal tail. The simplest model of Kinesin-1 activation posits that cargo binding to nonmotor regions relieves autoinhibition. In this study, we show that binding of the c-Jun N-terminal kinase–interacting protein 1 (JIP1) cargo protein is not sufficient to activate Kinesin-1. Because two regions of the Kinesin-1 tail are required for autoinhibition, we searched for a second molecule that contributes to activation of the motor. We identified fasciculation and elongation protein ζ1 (FEZ1) as a binding partner of kinesin heavy chain. We show that binding of JIP1 and FEZ1 to Kinesin-1 is sufficient to activate the motor for MT binding and motility. These results provide the first demonstration of the activation of a MT-based motor by cellular binding partners
The Keck Aperture Masking Experiment: Dust Enshrouded Red Giants
While the importance of dusty asymptotic giant branch (AGB) stars to galactic
chemical enrichment is widely recognised, a sophisticated understanding of the
dust formation and wind-driving mechanisms has proven elusive due in part to
the difficulty in spatially-resolving the dust formation regions themselves. We
have observed twenty dust-enshrouded AGB stars as part of the Keck Aperture
Masking Experiment, resolving all of them in multiple near-infrared bands
between 1.5 microns and 3.1 microns. We find 45% of the targets to show
measurable elongations that, when correcting for the greater distances of the
targets, would correspond to significantly asymmetric dust shells on par with
the well-known cases of IRC+10216 or CIT6. Using radiative transfer models, we
find the sublimation temperature of 1130 +- 90 K and 1170 +- 60 K for silicates
and amorphous carbon respectively, both somewhat lower than expected from
laboratory measurements and vastly below temperatures inferred from the inner
edge of YSO disks. The fact that O-rich and C-rich dust types showed the same
sublimation temperature was surprising as well. For the most optically-thick
shells (tau > 2 at 2.2 microns), the temperature profile of the inner dust
shell is observed to change substantially, an effect we suggest could arise
when individual dust clumps become optically-thick at the highest mass-loss
rates.Comment: accepted to Monthly Notices of the Royal Astronomical Societ
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